From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47F0EC433E6 for ; Tue, 12 Jan 2021 11:13:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EEB2323104 for ; Tue, 12 Jan 2021 11:13:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727745AbhALLM7 (ORCPT ); Tue, 12 Jan 2021 06:12:59 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34894 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726824AbhALLM5 (ORCPT ); Tue, 12 Jan 2021 06:12:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610449890; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v2hK43Fv/Oxk9V4fKnHoNGXpB/ifj+CAIGy8anHnl48=; b=Zimc1OBq5Z5L/jiqxol+uSKtSoSgka+c+/8JRNFJDMQLuirLKFPmxZMqaA1vyElu0e7ekA Pqqr697nMDwE2WdV2+cmvDaFFmRUBeUVLZ6jtXXRz/4Pxl/rv6JWdzvn2JrDrzqbj9zmQm LG7oad7LoA9XyjkSk+42DJICwfiIEe4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-45-SXf_gtTYOLCxwDdsktvtfw-1; Tue, 12 Jan 2021 06:11:26 -0500 X-MC-Unique: SXf_gtTYOLCxwDdsktvtfw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C3DA4BBEE1; Tue, 12 Jan 2021 11:11:24 +0000 (UTC) Received: from [10.36.115.140] (ovpn-115-140.ams2.redhat.com [10.36.115.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id D56AB60BE2; Tue, 12 Jan 2021 11:11:22 +0000 (UTC) Subject: Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one From: David Hildenbrand To: Muchun Song , mike.kravetz@oracle.com, akpm@linux-foundation.org Cc: n-horiguchi@ah.jp.nec.com, ak@linux.intel.com, mhocko@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yang Shi References: <20210110124017.86750-1-songmuchun@bytedance.com> <20210110124017.86750-2-songmuchun@bytedance.com> <1b39d654-0b8c-de3a-55d1-6ab8c2b2e0ba@redhat.com> Organization: Red Hat GmbH Message-ID: Date: Tue, 12 Jan 2021 12:11:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <1b39d654-0b8c-de3a-55d1-6ab8c2b2e0ba@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.01.21 12:00, David Hildenbrand wrote: > On 10.01.21 13:40, Muchun Song wrote: >> If the refcount is one when it is migrated, it means that the page >> was freed from under us. So we are done and do not need to migrate. >> >> This optimization is consistent with the regular pages, just like >> unmap_and_move() does. >> >> Signed-off-by: Muchun Song >> Reviewed-by: Mike Kravetz >> Acked-by: Yang Shi >> --- >> mm/migrate.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 4385f2fb5d18..a6631c4eb6a6 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, >> return -ENOSYS; >> } >> >> + if (page_count(hpage) == 1) { >> + /* page was freed from under us. So we are done. */ >> + putback_active_hugepage(hpage); >> + return MIGRATEPAGE_SUCCESS; >> + } >> + >> new_hpage = get_new_page(hpage, private); >> if (!new_hpage) >> return -ENOMEM; >> > > Question: What if called via alloc_contig_range() where we even want to > "migrate" free pages, meaning, relocate it? > To be more precise: a) We don't have dissolve_free_huge_pages() calls on the alloc_contig_range() path. So we *need* migration IIUC. b) dissolve_free_huge_pages() will fail if going below the reservation. In that case we really want to migrate free pages. This even applies to memory offlining. Either I am missing something important or this patch is more dangerous than it looks like. -- Thanks, David / dhildenb